AT&T engineered an unusual low-power antenna system inside a radio quiet zone at a snow resort in rural West Virginia, giving thousands of daily smartphone users network access for the first time.

Work on the multimillion-dollar solution started in 2013 and took months of testing with engineers at the National Radio Astronomy Observatory (NRAO) and staff at Snowshoe Mountain Ski Resort.

The custom-designed Distributed Antenna System (DAS) network went operational in 2015 and worked well for skiers over the past winter, according to Steven Little, senior radio access network engineer at AT&T.

Little compared AT&T’s deployment of 200 different indoor and outdoor antennas working at very low power to the technology equivalent of whispering in a library to avoid disturbing others. “Nobody has anything like it other than AT&T,” he said in an interview on Wednesday.